Blood pressure measurements in clinical setting are conventionally mainly based on the sphygmo-manometric occlusive arm-cuff, which is clumsy, uncomfortable and only allows for intermittent measurements at intervals of several minutes. Hence, there is a strong interest by the medical community in new technologies, which provide timely detection of critical changes of a patient's blood circulation status. A technical approach for early detection of critical blood pressure changes is based on the pulse wave velocity (PWV) technique, where surrogate markers of blood pressure are typically derived from a continuously monitored ECG waveform and plethysmograph like the signal of a single wavelength of from a SpO2 sensor. The measurement of the pulse wave velocity offers the opportunity to derive significant changes of arterial blood pressure at heart-beat frequency without applying an external pressure. It is common practice to use the pulse arrival time (PAT), which is defined as the time-delay between the R-peak of the QRS wave from the ECG and the arrival of the arterial pulse wave at the periphery, e.g. measured by a plethysmograhic sensor.
Conventionally, whenever a significant change in blood circulation is identified based on a measurement of the pulse arrival time from the ECG and the plethysmograhic sensor, a standard cuff-based blood pressure measurement is triggered automatically to confirm the change in blood pressure and to let the practitioner know it, when the patient's blood pressure is falling/increasing to critical level. However, in this way still a great number of cuff-based blood pressure measurement is triggered which would not have been necessary since actually no severe change in blood pressure of the patient has occurred.